Double action volume control



A. SENAUKE 1,894,794

DOUBLE ACTION VOLUME CONTROL Filed July 3. 1929 Jan. 17, 1933.

VT'1 6 J l3 1 I lNVENTOR ALEXANDER SENAUKE.

A m in ATTORN EY Patented Jan. 17, 1933 UNITED STATES PATENT OFFICE PORATION, OF BUFFALO, NEW YORK, A CORPORATION OF NEW YORK DOUBLE ACTION VOLUME CONTROL Application filed July 3,

This invention relates to means for controlling the level of energy supplied by a vacuum tube amplifier, and more particularly to means for simultaneously controlling the amount of signal energy supplied to the amplifier and the amount of amplificatlon produced therein.

In my prior application dated June 13, 1929, Serial Number 370,545, entitled Dual action volume control I have disclosed a sys tem of this general character which I have found gives very satisfactory results in most cases. There are, however, certain conditions under which I have found it advantageous to modify my previous system by incorporating the improvement hereinafter dlsclosed One object of this invention is to provide a system of volume control in which both the amount of signal energy delivered to the amplifier and the bias potential applied to the grid or grids is controlled by moving a single tap on a resistance, and in which an adequate voltage drop for bias purposes is secured while using a resistance which is low enough in value to give proper control of the input signal energy.

Still other objects and advantages 0t my inventlon will be apparent from thespecifica tion.

The single figure is a wiring diagram of a preferred form of my invention shown as applied to a single stage of tuned radio frequency amplification. In this figure reference character 1 denotes the antenna which is connected to one end of coil 2, and to the end 20 of resistance 19. The other end of coil 2 is connected to ground Coil 4 is in inductive relation to coil 2. with variable condenser 5 forms a tunable resonant circuit one side of which is connected to the control electrode or grid 6 of vacuum tube VTl, while the other side is grounded at 3. The cathode 7 is heated by the filament 8 which is supplied with current from a source not shown. The anode 9 is connected to the positive terminal of the B supply 14 through coil 10, which is coupled to coil 11. Coil 11 and condenser 12 form a second resonant circuit connected on one side to the grid 13 of a second vacuum tube not otherwise shown. The other side of 1929. Serial No. 375,869.

this second resonant circuit connects to ground 3. By-pass condenser 15 shunts the B supply, and is grounded at 3. By-pass condenser 16 is between the cathode 7 and ground 3. Resistances 18 and 19 are connected in series between the antenna 1, and the cathode 7. Movable tap 22 connects resistance 19 with ground 3. A bleeder resistance 17 connects the cathode 7 with the positive terminal of the B supply 14.

When the amplifier is in operation and the movable contact 22 brought to the end 21 of resistance 19, there will be a volta e drop across resistance 18 which will depend on the ohmic value of this resistance, and the amount of current flowing through it. The current which flows throu h this resistance is the sum of two currents, first the space current of the tube, and second the current which flows through the bleeder resistance 17. B a proper choice of values for resistances 17 and 18, I am able to secure a voltage drop across resistance 18 which will provide proper grid bias for normal operation of vacuum tube VTl. It will be noted that in this case all of resistance 19 shunts antenna coil 2, and that the reduction in signal voltage applied to the amplifier, will be comparatively small.

If new movable tap 22 be placed at the end 20 of resistance 19, the coil 2 will be shorted, and consequently almost no signal voltage will find its way to the amplifier. At the same time the grid bias potential will have been increased by the placing of resistance 19 in series with resistance 18 between cathode 7 and ground 3. If the value of resistance 19 and the amount of current flowing through it are properly chosen, the bias potential will have been increased to a point where little or no amplification will result. By making the value of this bias potential sufiiciently large a point can be reached where the tube actually reduces a signal applied to its grid. If contact 22 be moved from the end 20 towards the end 21 of resistance 19, that portion of resistance 19 which shunts coil 2 will be increased, while that portion of resistance 19 in series with resistance 18 between cathode and ground will be reduced. This will result in more signal 100 ALEXANDER SENAUKE, OF NEW YORK, N. Y., ASSIGNOB TO KING MANUFACTURING COE- I volta e being applied to the grid 0 of vacuum tube T1 and in a simultaneous decrease in its bias potential, which in turn will increase the amplifying action of the tube.

I have found that to function properly as an antenna shunt, resistance 19 should be in the order of 5000 to 10000 ohms. I h-avealsc found that a resistance of this order does not provide suflicient voltage drop for full a m plification control when the space current of only one tube is flowing through it. However, the addition of bleeder resistance 17 overcomes this difficulty, malting it possible to increase the current flowing between cathode and ground to an amount which will give the desired bias potential.

While I have shown and described certain preferred embodiments of my invention, it

will be understood that modifications and changes may be made without departing from the spirit and scope. of my invention, as will be understood by those skilled in the art.

I claim:

1. In an amplifier system in combination, a thermionic vacuum tube, a source of anode potential, a path through which the anode current flows, a second path through which current flows from the source of anode potential, a resistance in said second path, and a resistance common to both said current paths, means for applying the volta e drop across said two resistances as a biasipotential to the grid of said vacuum tube, an input circuit associated with said vacuum tube, a third resistance in shunt with said input circuit, and means for simultaneously varying said last named resistance and said common resistance.

2. In an amplifier system in combination, a thermionic vacuum tube having an anode, a cathode and a control electrode, an input circuit and an output circuit associated therewith, a variable resistance shunting said inut circuit, a blecdcr resistance connected tween said cathode and a point in said output circuit substantially at anode potential, 9. second variable resistance traversed by the space current of said tube, and by said bleeder resistance current, means for applying the voltage drop through said last-named variable resistance as a bias potential to the grid of said tube and means for simultaneously varying both said variable resistances.

3. In an amplifier system in combination, a thermionic vacuum tube, a source of anode potential, a path through which the anode current flows, a second path through which current flows from the source of anode potential, a resistance common to both paths, and means for applying the voltage drop across said resistance as a bias potential to the grid of said vacuum tube, an input circ'uit associated with said vacuum tube, a. re-

sistance in shunt with said input circuit, and

means for simultaneously increasing one of said resistances and decreasing the other.

4. In an amplifier system in combination, a thermionic vacuum tube having an anode, a cathode and a control electrode, an in ut circuit and an output circuit associate therewith, a variable resistance shunting said input circuit, a bleeder resistance connected between said cathode and a point in said output circuit substantially at anode potential, a second variable resistance traversed by the space current of said tube, and by said bleeder resistance current, means for applying the voltage drop through said last-named variable resistance as a bias potenial .to the grid of said tube and means for simultaneously varying both said variable resistances, simultaneously and in an opposite sense.

5. In an amplifier system, in combination, a vacuum tube amplifier, an input circuit associated therewith, a variable resistance in shunt therewith, a second variable resistance traversed by the space current of said tube, means for passing additional current through said last-named resistance, means for applying the voltage drop developed in said lastnamed resistance as a bias potential to the grid of said tube and means for varying both said resistances simultaneously.

6. In an amplifier system, in combination, a vacuum tube amplifier, an input circuit associated therewith, a variable resistance in shunt therewith, a second variable resistance traversed by the space current ofv said tube, means for passing additional current through said last-named resistance, means for applying the voltage drop developed in said lastnamed resistance as a bias potential to the grid of said tube and means for simultaneously increasing one of said resistances and decreasing the other.

7. In an amplifier system, in combination, a vacuum tube amplifier, an input circuit associated therewith, aresistance having one portion thereof traversed by the space current of said tube, means for passing additional current through said resistance, means for applying the voltage drop through said one portion of said resistance as a bias potential to the grid of said tube, said resistance having another portion in shunt with said input circuit and a connection to said resistance shiftable to vary the value of said portions inversely.

ALEXANDER SENAUKE. 

